Tensioning and anchoring of cables in concrete or similar structures



March 20? 1945. 2,371,882

TENSIONING AND ANCHORING 0F CABLES IN CONCRETE 0R SIMILAR STRCTURE E.FREYSSINET Filed Feb. l, 1941 .rlll lllllllll.; ."5

Patented Mar. 20, 1945 TENSIONING AND ANCHORING 0F CABLES 1N CONCRETE 0RSIMILAR, STRUCTURES Eugne Freyssinet, Neullly-sur-8eine, France: vestedin the Alien Property Custodian application February 1, 1941, serais.:11,041

In France October Z8, 1940 s claims.' (ci. za-5o) It is well known thatthe characteristics of reenforced concrete constructions arevconsiderably improved by artificially submitting the reenforcements topreliminary tensile stresses sumciently high in order that the concreteis subjected to permanent compressive strains (see my U. S. Patent No.2,080,074). The tension may be lmparted to the reenforcements eitherbefore the setting of the concrete, or after its setting and hardening,on condition that, in the latter case, provision be made for suitablemeans to prevent the adhesion of the steel to the concrete, in order toallow the elongation of this steel embedded in the set and hardenedconcrete.

Such reenforcements are frequently constituted by means of steel wirecables having a high elastic limit. In general, the devices used for tensioning and anchoring comprise projections exterior to the concrete tobe compressed, and do not allow the compressive stresses to be increasedbeyond a certain maximum which is very much less than the resistance ofthe concrete to be compressed. f

My invention has for its object a process and a device for tensioningand anchoring cables, said device being incorporated in the concrete tobe compressed without requiring any projection or addition to theconcrete for the purpose of concealing the anchorings. This deviceallows moreover the increasing of the preliminary stresses to theyielding point of the concrete. y This process is applicable inparticular to pre stressed concrete constructions in the case where thetension is imparted to the reenforcements after the setting of theconcrete, although it can also be utilized in constructions other thanconcrete or in concrete constructions when the reenforcements aretensioned before the setting of the concrete.

In what follows, only the application of the process to concrete will beconsidered for the sake of simplicity, it being understood that theother applications also fall within the scope of my invention.

wires and nally the releasing of the tension exerted by the jack, thetensionof the wires is maintained bythe weding. in the female c'one. ofthe male cone composed of the wires and the wedgesl pressed one againstthe other.

'I'he anchoring arrangement comprises then essentially a tunnel-shapedcavity, the inner Surface of which is capable of withstanding thestresses of expansion imrted to it by the wedging of the male cone, andmeans for transferring to the concrete to be compressed that componentof these stresses which is parallel ,to the cable.

It may be made up, for example, of an element of cast steel, embedded inthe concrete, comprising, in the first place, a funnel-shaped cavity theinside of which is machined to obtain the desired shape and, in thesecond place, one or more surfaces bearing on the concrete, of sumcientares to subject the concrete to sustainable stresses.

But the same results may be obtained more economically by havingrecourse to means proper to reenforced concrete. The truncated cone maybe hollowed 'out in the concrete itself and the wall of this cavityrendered capable of resisting the stresses of expansion by embedding inthe concrete a first reenforcement which may consist in a truncated tubeor in a. coil formed by helicoid turns of steel wire, having preferablya high elastic limit, or in a combination of both means. Thetransmission of the strains from this first reenforcement or coil to theconcrete to be compressed may be ensured by a second transversereenforcement of the concrete in which it is embedded. This secondreeniorcement con. sists, for example, of a coil of'steel wire helicallywound and located at a certain distance from the rst one.

In order to ensure a better achievement of the truncated aperture orcavity, it is possible to pour in advance concrete slabs, each providedwith a cavity and with the reenforcing coil or coils.

These slabs may contain one or more anchoring also a sectional view of apart of an hydraulic jack utilized in tensioning a cable.

Figures 2 to 4 are transverse sectional views along axes II-II, III-IIIand IV-IV of Fig. 1.

Figure 5 represents a fragmentary plan view of the device utilized forthe fixation of the wires to the ,i ack.

Figure 6 shows a fragmentary sectional view showing another embodimentof an anchoring block.

Figure 7 shows diagrammatically in longitudinal section one extremityonly of a pre-stressed concrete beam, provided with anchoring blocksconstructed in accordance with my invention.

Figure 8 represents a sectional view of a prestressed concrete beamprovided with these anchoring blocks.

spread out and pressed against the inner wall a-b of the truncated coneand between these wires steel wedges 8 are set. The sides of thesewedges are provided with cylindrical grooves la corresponding to theshape of the wires, so that these wedges, inserted between the wires aremaintained by the latter and form together with them a sort of male conewhich comes to bear against the inner wall af--b of the female cone.

For the operation of tensioning, in the case under consideration, anhydraulic Jack is utilized, the piston 9 of which can bear against head2. This piston is provided with slots l0 equal in number to that of thewires of the cable and In the example illustrated by the drawing, the

application of the anchoring device to the ten# sionlng of thereenforcements of a concrete construction has been presumed to occurafter the setting and hardening of the concrete. Each reenforcexnent.composed of a cable. is set in a sheath I which is set in place in themolds before the pouring of the concrete and serves to insulate the saidreenforcement from the concrete in order to allow the elongation of thereenforcement. l

This sheath may consist of a tube of steel or of other material,preferably thin sheet steel rolled into a cylindrical shape, and claspedby bending back the edges. It may even consist merely of a plain coatingof a greasy substance or of a plastic one of low melting point,basically composed of bitumen, pitch or rubber which is applied to thewires. This coating can be protected by swathing with paper or otherfibres impregnated with substances of the same nature.

Each extremity of a reenforcement or only one of the extremities, if theother be securely fastened to the concrete by any well known anchoringsystem, is inserted in the anchoring slab or block, which is going to bedescribed with respect to Figures 1 to 5.

This slab or block comprises a high-resistance concrete mass 2, havingtherein an aperture or cavity the contour of which is generated by acomplete revolution of the straight line af-b about the axis :Izx, whichforms with line a-b an angle having a tangent of approximately 55, thesaid straight line being joined to the generant of tube I parallel toaxis :cby a curve b-c.

About the wall of the orice so formed, a steel reenforcemcnt 3 isembedded in the concrete 2. This reenforcement may be composed ofhelicold turns of asteel wire having a high elastic limit so that thecoil thus formed can resist the strains to which the wall of the cavityis subjected in operation. In the example described, the slab or blockhas the form of a solid of revolution composed of a head 2a and of aprolongation 2b having the shape of a. truncated cone which is joined tothe extremity of sheath I by a junction Ia of tissue or of paperimpregnated with a plastic substance, such as tape. About the head 2a,the concrete is reenforced by a second coil 4 which may be of softsteel.

The concrete 5 of the construction or of the piece to be built is pouredabout tube I and about the block taking care to allow provision for ahole 6 through which it will be possible to have access to the extremityof the cable (passing through head 2) from the exterior of theconstruction. The wires 1 composing this cable areused for the passageof the wires, whereas the cylinder II comprises devices for thefastening of these wires. These devices consist in trapezoidal slots I2provided on a rim I3 of the cylinder I I and of wedges I4 which areinserted in these slots between two wires of the cable; the number ofslots is consequently equal to half the number of wires, which conditionrequires, in this embodiment, the use of cables having an even number ofwires.

In the interior of piston 9, a second piston I5 may displace itself andcome to bear on the extremity of wedges 8 by means of a small plate I6provided with slots for the passage of the wires. Piston 9 is providedwith a hollow Il the diameter of which corresponds to that of the smallplate.

The jack being disposed as shown in Fig. 1 and pressure being admittedin cylinder II, this cylinder draws away from piston 9 and tensionswires l. The wedges follow the movement of the wires at the start untilthey run against plate I6, they then leave between themselves suillcientclearance to allow the wires, pulled by cylinder I I, to slide freely.

In zone b-c of the anchoring head, the wires press against the concreteof this head and to limit their friction, this zone is lined -by acasing I8 of tinplate for example.

When the tension stress, which can be determined from the pressure incylinder II, at-

tains the desired value, the pressure is maintained in the cylinder, andpiston I5 is put under pressure. The latter obtains a compression of thewedges between the wires by expanding the male cone and by compressingit against the inner wall of the female cone.

The pressure in the two jacks may then be released, the wires withdrawnfrom slots I2 of the jack and the latter removed; the anchoring thusbeing finished. The tensioned cable. subjected no longer to any externalforce, wedges the male cone composed of the Wires and of the wedges inthe female cone. The wires could, as a matter of fact, slip between thewedges only if the angle of friction between wedges anf wires fell belowa value such that tan.

In order that the anchoring may resist it steel coil 3 appears. It mustbear the stresses which make with the axis of the cone an angle which isthe sum of the angle at the top of the cone and of the angle of frictionsteel on concrete.

Under the action of the tensioned cable, there results, finally, anequilibrium between the deformations of coils 3 and l, of the concrete 2and that of the underlying concrete 5, an equilibrium which allows arelatively large deformation of coil 3, a relativelyv much smallerdeformation of coil 4 and a triple compression stress accompanied by aplastic deformation of the concrete 2 with the production of isostaticlines such as UV, XY.

In that portion of the concrete where the head bears on the concrete 5of the construction, this concrete may be profitably reenforced byrectanguiar reenforcements.

It is to be noted that nothing prevents the jack from being set in placefor operation a second time; the wires may be tensioned again by meansof the jack, the wedges loosened, the initial tension increased (or evenreduced, if a means for preventing the wedges from jamming by themselvesbe provided). So the tensioning operations may be effected in aprogressive manner, they may be rectified, in case of error, etc.

Oncethe tensioning has been completed, hole t may' be stopped up byconcrete, and the extremities of projecting wires embedded in concretewhich ils up a small recess provided forin the mass subjected topreliminary stresses, which process oers the advantage of an additionalsecurity by opposing the vslipping of the wires against the wedgingmeans.

Figure 6 shows a cast steel anchoring block 2a provided with a femalecone 2b, the surface 2c, 2d of which block bears on the concrete andtransmits the strains developed by the tensioned cable. This anchoringblock is utilized in the same manner as that described for the concreteslab.

Figure 7 shows the extremity of a beam pro- 4vided with reenforcements dset in sheaths, the

reenforcements being tensioned and anchored as has just been described.The anchoring heads e are located at the extremities of thereenforcements in the housings provided for, prior to the pouring of theconcrete.

The block may have also a square or rectangu` lar cross-section andcomprise anchoring devices for several cables. In this case, coils i maybe replaced by rectangular. reenforcements perpen A ing the tensioningoperation) and the final tension are both directed along the same axisand act on the same substance, which conditions allow the compressing ofthe entire surface of the concrete to a maximum stress consistent withits resistance.

The invention is not limited to the case where the tensioning iseffected after hardening of the concrete.

The concrete in which the tensioned reenforcements are embedded may bepoured only after the tensioning of these reenforcements, on conditionthat fulcrums for the anchoring blocks be available while the tensioningis in process; these fulcrums can be chosen on the molds or on a portionof the concrete of the construction in which the reenforcements are notembedded, which concrete is poured in advance and has already hardenedprior to the tensioning.

For example, in the case of a beam having a cross-section as representedon Figure 8, it is possible, after setting in place reenforcements d andthe anchoring blocks, to pour first the concrete represented by thehatchings in which concrete the reenforcements are embedded only at theextremities of the beam. When this concrete has hardened, thosereenforcements, the anhoring blocks e of which utilize the saidconcrete, as fulcrum, may then be tensioned. Once the tension andanchoring operations are completed, the rest of the concrete (see thedotted lines in Fig. 8) may be poured about the tensioned reenforcementsd. y

The device for tensioning and anchoring constructed according Ato myinvention also odors a practical means of obtaining, by tensionedreenforcements, a uniting into a single structure of distinct concretepieces laid out end to end for example. The tensioning of thereenforcements which will be placed for example in the holes provided inthese pieces, will result in their compression one against the other.

it is obvious that the embodiments which have just been describedconstitute only examples and that these can be departed from withoutaffecting the scope of the invention. The invention is applicable notonly to the case where the elements of the cable to be tensioned consistin simple wires, but also to the case where these elements consist ofstrands or of groups of wires. In the claims hereunder, the word wiremust be understood as designing not only a single wire properlyspeaking, but also a group of wires or a strand.

What I claim is:

l. A process for anchoring an end of an elongated reinforcement for astructural member, which reinforcement includes a group of wires, saidprocess comprislng, providing a funnel-` shaped cavity in saidstructural member with its larger end facing outwardly away from themember, inserting said reinforcement wires within said member withportions adjacent the ends thereof Within said cavity, spreading out thewires in spaced relationship against the wall of the cavity, tensioningthe wires by the application of an external force, and forcing wedgesbetween each pair of adjacent wires, the force applied to the wedgesbeing sufficient to produce enough friction between the wires and thewedges l to withstand the ,tension in the wires, after which v saidexternal force is discontinued.

2. A process for anchoring an end of an elongated reinforcement for aconcrete member, which reinforcement includes a bundle of wires, saidprocess comprising, providing a funnelshaped cavity in said concretemember with its larger end facing outwardly away from the member, liningthe wall of the larger end of the cavity with reinforcing metalinserting said reinforcement wires within said member with portionsadjacent to the ends thereof disposed within 4 aaneen the larger end ofsaid cavity, spreading out the wires in spaced relationship againstlining of the larger end of the cavity, tensioning the wires by theapplication of an external force, and applying wedges between each pairof adjacent wires, with 'sufficient force to produce an elasticexpansion in the metal lining and sufiicient friction between the wedgesand wires to anchor them in place, after which said external force isdiscontinued.

3. A process for anchoring an end of an elongated reinforcement for aconcrete member. which reinforcement includes a bundle of wires, saidprocess comprising: enclosing said wires ad- 'jacent their ends within ahollow funnel-shaped steel member, said hollow member having its largeropening facing in the direction of said ends, pouring concrete aboutsaid hollow member, spreading out the wires in spaced relationshipagainst the inner surface of the hollow member, placing wedges betweeneacn pair of adjacent wires, tensioning the wires after the' hardeningof the concrete by exerting a tensile stress on their extremities whichproject out from the concrete using said concrete as a fulcrum, thenwhile maintaining the tensile stress, applying the wedges toward thesmaller end of said hollow member between adjacent wires with sufncientforce to produce an elastic expansion of said hollow member andsuincient friction between the wedges and wires to anchor them inplace', after which said external tensile stress is discontinued.

4. In a concrete or similar structure, in combination, a mass ofconcrete or the like, a longitudinally tensioned reinforcement passingtherethrough and comprising an elongated member having a divided endportion comprising a plurality of strands, the mass of concrete beingprovided with a conical outwardly flared cavity surrounding saidstrands, said strands being spread to engage the wall of the cavity incircumferentially spaced relationship, and wedges forced between eachadjacent pair of strands in a, manner to hold the strands tofrictionallyengage with the wall of the cavity.

5. A concrete or similar structure having means for anchoring the endportions of a bundle of tensioned wires constituting reinforcement ofsaid structure, said means comprising, in combination, a concrete parthaving a funnelf shaped cavity therein, the wall of which surrounds saidbundle of wires adjacent the said end portions, said cavity having itslarger end facing in the direction of said end portions and away fromsaid concrete structure, a tubular metal reinforcement embedded in saidconcrete part and spacedly encircling said cavity, said reinforcementbeing tapered oppositely to and surrounding the larger end of thecavity, said wires being spread against the surface of said larger endof the cavity, and wedges forced between each pair of adjacent wires ina manner to tension the wires around the wall of the cavity.

6. A concrete or similar structure, according to claim 5, wherein saidtubular metal reinforcement consists of a helically wound hard steelwire.

7. A concrete or similar structure having means for anchoring theextremity of a bundle of tensioned wires constituting reinforcement ofsaid structure, said means comprising, in combinaton, a concrete blockembedded in said structure and provided with a funnel-shaped cavityserving as a housing for a portion of said bundle of wires adjacent tothe extremity thereof, said cavity having its larger end facing in thedirection of said extremity and away from said structure, a steelreinforcement lining the wall of the larger end of said cavity, a secondsteel reinforcement embedded in the block and spacedly surrounding saidlining and located adjacent to the outer periphery of said block,bearing surfaces on said block facing said structure in a direction awayfrom said extremity of the bundle of tensioned wires and arranged totransmit compressive strains to the structure under the in-' iuence ofthe tension in said wires, said wires being deected to lie along thelining( in circumferentially spaced relation, and wedges forced betweeneach pair of adjacent wires in a manner to tension said lining.

8. A, concrete or similar structure having means for anchoring theextremity of a bundle of tensioned wires constituting reinforcement ofsaid structure, said means comprising, in combination, a concrete blockembedded in said structure and provided with a funnel-shaped cavityserving as a housing for a portion of said bundle of wires adjacent tothe extremity thereof, said cavity having its larger end facing in thedirection of said extremity and away from said structure, a steelreinforcement lining the wall of the larger end of said cavity, a secondsteel reinforcement embedded in the block and spacedly surrounding saidlining and located adjacent to the outer periphery of said block,bearing surfaces on said block facing said structure in a direction awayfrom said extremity of the bundle of tensioned wires and arranged totransmit compressive strains to the structure under the influence of thetension in said wires, said wires being deflected to lie along thelining in circumferentially spaced relation, and wedges forced betweeneach pair of adjacent wires and forcing the wires against said liningwith sufficient pressure to place said lining and the surroundingconcrete .under tension.

EUGNE magasiner.

